Semi-empirical metallicity calibrations based on ultraviolet emission lines of type-2 AGNs

DORS, O L; MONTEIRO, A F; CARDACI, M V; HÄGELE, G F; KRABBE, A C

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2019

0035-8711

We derived two semi-empirical calibrations between the metallicity of the Narrow Line Region (NLR) of type-2 Active Galactic Nuclei and the restframe of the Nvλ1240/Heiiλ1640, C43=log[(Civλ1549+Ciii]λ1909)/Heiiλ1640] and Ciii]λ1909/Civλ1549 emission-line intensity ratios. A metallicity-independent calibration between the ionization parameter and the Ciii]λ1909/Civλ1549 emission-lines ratio was also derived. These calibrations were obtained comparing ratios of measured UV emission-line intensities, compiled from the literature, for a sample of 77 objects(redshift 0 < z < 3.8) with those predicted by a grid of photoionization models built with the Cloudy code. Using the derived calibrations, it was possible to show that the metallicity estimations for NLRs are lower by a factor of about 2-3 than those for Broad Line Regions (BLRs). Besides we confirmed the recent result of the existence ofa relation between the stellar mass of the host galaxy and its NLR metallicity. We also derived a M −Z relation for the objects in our sample at 1.6 < z < 3.8. This relation seems to follow the same trend as the ones estimated for Star Forming galaxies of similar high redshifts but for higher masses.